Many minimally invasive medical procedures are performed using a catheter with a lumen. For example, in angioplasty, a balloon is inflated using saline solution conveyed through a lumen. In many cases it is desirable to inject medicine or radio-opaque dyes through a catheter's lumen. In some procedures, a tool is guided through the lumen. After the use of the tool is completed, the tool is retracted and may be replaced by another tool.
U.S. Pat. Nos. 5,480,422, 5,383,454, 5,295,486 and 5,437,277 and PCT application PCT/US95/01103, the disclosures of which are incorporated herein by reference, describe a few of the many types of position sensing tips for catheters. The position sensor in the catheter tip allows the physician to monitor location of the tip within the body without continually imaging the body and catheter. This capability can significantly reduce the radiation exposure of the patient and of the physician. For many position sensors size is an important factor. In some cases, the larger the sensor the more precise the position estimate. The maximum size of the position sensor typically is limited by the diameter of the catheter. In general, catheters with a smaller diameter are more flexible and can be used in a larger portion of the vascular system than catheters with a large diameter.
It is difficult to accommodate both a large lumen and a position sensor in the tip of a catheter, since the position sensor typically occupies almost the entire cross-section of the catheter.